2nd Gen Cummins heater temp differences between trucks

[01_Cummins_4x4]

In the two previous 99 Dodge Cummins 2500 4x4 pickups that I had, once I replaced the heater core, evaporator core, cleaned the hvac box, new 190* thermostat, new blower fan motor, both of those pickups would roast me out of the cab if I ran the heater on high for too long.

 

On this 01 Cummins 4x4, it has a new radiator, new water pump, new heater and evaporator cores, cleaned the hvac box, new heatertreater transposer for the temp blend door, new blower motor rheostat, and new NAPA 190* thermostat. The only thing that I haven't changed is the heater blower motor on this pickup, but I have good airflow and my engine temp is running 190*, but this truck will not roast me out when it gets too cold outside. I just installed a geno's garage winter grille cover over the radiator, condenser, and intercooler, but that didn't make it do anything different and the truck still runs at 190*.

 

Anyone have any other ideas to fix this issue?  I know this is a very common issue in the 2nd gen dodge pickups and hopefully someone has some ideas as what to do next to fix it.

 

Thanks!

 

Doug

 

[JAG1]

Turning the upper knob to air conditioning mode while lower knob is on high heat helps some because it does not take in outside air in this mode. I been doing that.

[IBMobile]

May be the heater blend door actuator is not in sync with the dash heater control and need to be recalibrated.

[01_Cummins_4x4]

I recalibrated it according the instructions that come with the heatertreater transposer. I did the same thing with my Dad's 02 Cummins after I put a heatertreater transposer in it.

[Haggar]

You could try to measure the temperature of the water going into and out of the heat exchanger.   (use thermocouples on the metal tubing with lots of insulation around it so you get good readings)

 

If the water temp is the same in and out, then you know the air is not blowing well through the exchanger.  If the temperature is very different, you know that not enough water is passing through the exchanger and that there is a coolant flow restriction somewhere.

 

I would expect 5 to 10 degrees temperature differential.  I am not certain of this at all.  I have not needed to make these measurements yet.

 

In my 01 I swear the replacement heater core did similar to yours.  The replacement was not as hot as the original....  It not as important in my part of the country as it is in your part though...

 

GL  HTH

 

Hag

[Mopar1973Man]

Correct the bigger the difference of temperature the hotter it will be in the cab. The hose out of the head is the supply of hot coolant. Then the hose to the metal tube is return. This should be notably cooler.

[JAG1]

Some guys figured out how to close off the outside air door with an added control, keeping the cold air from coming in but, I found going to A/C mode helps enough for me.

[01_Cummins_4x4]

Right after I shutoff my pickup in my shop I used my infrared thermometer to see what my heater hoses are at. The hot side towards the engine was 177° and the return hose was at 142°.

 

I didn't think to check them until after I shut it down.

Edited January 8, 2022 by 01_Cummins_4x4

[Haggar]

That sounds good really (the temp differential).  But, the incoming temperature sounds low.  What thermostat are you running?    The incoming temperature if you are running a 190, should be closer to 200.   (This could be your measuring method also.  IR thermometers read an average temperature over an area.  unless you have a good one that will give you an average and a peak also...)  That is why i mentioned the thermocouple and insulation.

Now, throw a thermometer in your closest outlet vent and compare it to the ambient temperature in your cab.   minus some losses, you might see this 30 degree difference.  

If the output is significantly lower than the temperature split, the system could be pulling in too much outside air.  You could try removing the AC compressor relay (so compressor does not actually run the AC), and running the system on Max AC.  (this closes/reduces the outside makeup air to a minimum) and see if that helps.

 

GL

Hag

[01_Cummins_4x4]

I'm running a brand new NAPA 190* t-stat. I installed it at the same time I installed a new Fel-Pro head gasket and head studs.

 

Running down the road my temperature gets to 190* when it's fully warmed up.

[JAG1]

@HaggarDoesn't having the lower knob on high temp keep the compressor from going on? Like a thermostat?

[Haggar]

@JAG1 unfortunately no.  This system was too simple.  (but not simple enough to just have a stupid compressor button.....my explorer sport has a compressor button, but when you pick defrost modes it will bypass the stupid button.....  sorry I digress.....)

Notice the clutch relay is forced "on" electrically by our selection of modes.   The heater doors are controlled by vacuum, but in certain positions the clutch is engaged irregardless of what temperature we would like.   I know why they do this, they are trying to remove the humidity so your windows won't fog as easily, but there are just times when I think I am smarter than they are, but apparently not.....  lol

 

Hag

[Tractorman]

41 minutes ago, JAG1 said:

Doesn't having the lower knob on high temp keep the compressor from going on? Like a thermostat?

 

No.  The operator cannot control the cycling of the AC compressor.  There are only three positions in the upper control switch that disable the AC compressor circuit.  They are OFF, and the first two positions clockwise of the 12 O'clock position.  All of the other five positions activate the AC compressor circuit.

 

The lower knob (temperature control) controls the blend door position only.  It knows nothing else.  The blend door must be able to reach its full extent of travel in both directions.  At its extent in one direction, the blend door seals so that all air flow bypasses around the heater core.  At its extent in the other direction, the blend door seals the bypass and all airflow must travel through the heater core.  Any setting of the lower knob (temperature control) between its extents will adjust the blend door to allow air to flow around and through the heater core relative to the control knob's position.

 

The blend door operation is key and could very well be his problem.

 

The heater core in these trucks have more than sufficient capacity to easily heat the cab, even in below zero weather - far below the approximate 35 degree evaporator core temperature when the AC compressor is operating.

 

I run a 180° thermostat and I have no issues heating the cab.  I live on the other side of the Blue Mountains from @01_Cummins_4x4.  Much colder on this side.

 

- John

 

 

[IBMobile]

A few years back I helped a member with a wire diagram bypassing the vent control of the AC and install a manual on/off switch for the compressor.  I can dig it up if anyone is interested. 

[01_Cummins_4x4]

@Tractorman - How can I check the temperature blend door for full range of motion? I already calibrated the actuator per the heatertreater.net website when I installed their transposer.

 

I'm not pulling the HVAC box out to check it, so do I need to cut a window in the HVAC box to verify that the blend door is moving all the way in both directions, and then fabricate a cover to fit over the window that I cut into the box?

 

I have a problem with the AC on this truck as well, in that it won't blow cold for very long and it turns to lukewarm air even with a brand new evaporator core, vacuumed down properly with no leak detected and then 2# of R134 injected into the AC system.

 

Thanks,

 

Doug

[Tractorman]

3 hours ago, 01_Cummins_4x4 said:

How can I check the temperature blend door for full range of motion?

 

The only way to do that without removing the dash is to remove the blend door motor and interposer.  You can then manually operate the blend door to ensure it travels to its full extent in both directions.  Have your engine to operating temperature so you can test the heat output manually.  The video below will show you how to get to that point.

 

- John

 

 

 

 

[01_Cummins_4x4]

That's the video I watched when I installed their transposer, and recalibrated my actuator. 

 

 

[Mopar1973Man]

I've got the best heater of you all I get roughly 160*F temps out of the center vents at ZERO degrees outside. Then when I measure the hot and cold lines from the firewall. I've got 195*F going in and about 110*F coming back out. This shows that majority of my heater is transferred into the air of the cabin. Again I have zero lime scale blooms in the radiator or heater core so heat transfer is high for me. The biggest thing is keeping the coolant system flushed out on schedule and reloaded with fresh coolant every 3 year or about 75k miles. Don't trust that extended life coolants because with diesel every time you crank that engine over you charging the coolant up with high current after awhile the coolant gains a voltage this is when it becoming corrosive and pH level are drifting away from 7-8 pH. Just because it looks clean doesn't mean it is good yet.

[01_Cummins_4x4]

Just as soon as I got home and parked my truck in my shop, I popped the hood and scanned both heater hoses headed towards the heater core. The inside hose which is going to the driver's side tube of heater core was at 178* and the outside hose going to the passenger side tube of the heater core was at 172*.

 

I have a brand new heater core, brand new NAPA 190* t-stat, brand new water pump, and brand new radiator that is clean (new looking on the inside with no scale and new looking on the outside). New antifreeze was installed when replacing the head gasket and t-stat a couple months ago.

 

I don't see how the heater core could be plugged up with all new components.

 

 

[Mopar1973Man]

Measure with the engine running and the heater fan on HI. If it shut down the numbers will drift together in a short order. 

 

 

 

Edited January 11, 2022 by Mopar1973Man